Apparatus and method for determining a time resource unit

ABSTRACT

A method for transmitting an uplink signal is discussed. The method performed by a narrowband-internet of things (NB-IoT) device includes determining a time resource unit based on an uplink subcarrier spacing for transmitting the uplink signal; and transmitting the uplink signal on the time resource unit to a base station. Further, the time resource unit includes one or more slots including a plurality of symbols, based on the uplink subcarrier spacing, a predetermined time period in the one or more slots is not used for the transmission of the uplink signal, and the uplink carrier spacing includes 3.75 kHz.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of co-pending U.S. patent applicationSer. No. 15/579,421 filed on Dec. 4, 2017, which is the National Phaseof PCT International Application No. PCT/KR2016/006233 filed on Jun. 13,2016, which claims the priority benefit under 35 U.S.C. § 119(e) to U.S.Provisional Application Nos. 62/278,975 filed on Jan. 14, 2016,62/217,014 filed on Sep. 10, 2015, 62/184,229 filed on Jun. 24, 2015 and62/182,646 filed on Jun. 22, 2015, all of which are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to mobile communication.

Discussion of the Related Art

3rd generation partnership project (3GPP) long term evolution (LTE)evolved from a universal mobile telecommunications system (UMTS) isintroduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequencydivision multiple access (OFDMA) in a downlink, and uses singlecarrier-frequency division multiple access (SC-FDMA) in an uplink. The3GPP LTE employs multiple input multiple output (MIMO) having up to fourantennas. In recent years, there is an ongoing discussion on 3GPPLTE-advanced (LTE-A) evolved from the 3GPP LTE.

As disclosed in 3GPP TS 36.211 V10.4.0 (2011-12) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 10)”, a physical channel of LTE may be classified into adownlink channel, i.e., a PDSCH (Physical Downlink Shared Channel) and aPDCCH (Physical Downlink Control Channel), and an uplink channel, i.e.,a PUSCH (Physical Uplink Shared Channel) and a PUCCH (Physical UplinkControl Channel).

Recently, IoT (Internet of Things) communication has attractedattention. The IoT refers to communications that do not involve humaninteraction. There is a dissection about trying to accommodate such IoTcommunications in a cellular-based LTE system.

However, since the legacy LTE system has been designed for the purposeof supporting high-speed data communication, such an LTE system has beenregarded as an expensive communication system.

However, the IoT communication is required to be implemented at a lowprice because of its characteristics, so that it may be widely used.

Therefore, there have been discussions to reduce the bandwidth of theIoT communication for the sake of cost reduction. However, in order toreduce the bandwidth, the structure of the frame in the time domain mustbe newly designed. However, there has been no discussion about this yet.In addition, when the structure of the frame is newly designed, it isnecessary to newly consider the interference problem with neighboringlegacy LTE terminals.

SUMMARY OF THE INVENTION

Accordingly, a disclosure of the present specification has been made inan effort to solve the aforementioned problem.

To achieve the foregoing purposes, the disclosure of the presentinvention proposes a method for transmitting an uplink channel. Themethod may be performed by a narrowband-internet of things (NB-IoT)device and comprise: determining an uplink subcarrier spacing fortransmitting the uplink channel; determining a subframe length based onthe uplink subcarrier spacing; transmitting the uplink channel on asubframe having the determined length. A last portion of the subframemay be excepted for transmitting the uplink channel.

In one embodiment, the subcarrier spacing is determined to be 3.75 kHzor 15 kHz.

In one embodiment, when the subcarrier spacing is 3.75 kHz, the subframelength is determined to be 2 ms; or when the subcarrier spacing is 15kHz, the subframe length is determined to be 1 ms.

In one embodiment, the last portion is excluded for transmission of theuplink channel only when the last portion is overlapped with a temporalresource used for transmission of a sounding reference signal (SRS) by aLTE-based UE adjacent to the NB IoT device.

In one embodiment, the last portion is excluded for transmission of theuplink channel to secure the SRS transmission by the LTE-based UE.

In one embodiment, the method further comprises receiving information onthe SRS from a cell to which the LTE-based UE belongs.

In another aspect for achieving the purposes, there is provided anarrowband-internet of things (NB-IoT) device configured fortransmitting an uplink channel, the device comprising: a transmissionand reception unit configured to transmit and receive a radio signal;and a processor connected to the unit, wherein the processor isconfigured for: determining a spacing between uplink subcarriers usedfor transmitting the uplink channel; determining a subframe length basedon the uplink subcarrier spacing; controlling the transmission andreception unit to transmit the uplink channel on a subframe having thedetermined length, wherein a last portion of the subframe is exceptedfor transmitting the uplink channel.

According to the disclosure of the present specification, the problemsof the above-described prior art are solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a wireless communication system.

FIG. 2 illustrates a structure of a radio frame according to FDD in 3GPPLTE.

FIG. 3 illustrates a structure of a downlink radio frame according toTDD in the 3GPP LTE.

FIG. 4 is an exemplary diagram illustrating a resource grid for oneuplink or downlink slot in the 3GPP LTE.

FIG. 5 is a flowchart illustrating a random access procedure in 3GPPLTE.

FIG. 6A shows an example of IoT (Internet of Things) communication.

FIG. 6B is an example of a cell coverage extension or enhancement for anIoT device.

FIGS. 7A and 7B are views illustrating examples of a sub-band in whichan IoT device operates.

FIG. 8 shows an example of a time resource used for NB-IoT on M-framesbasis.

FIG. 9 shows another example of a time resource and a frequency resourcethat may be used for an NB IoT device.

FIG. 10 shows a first example in which RACHs are multiplexed by aplurality of NB-IoT devices.

FIG. 11 shows an example in which PRACH resources per a subframe arefour when a NB-IoT (or NB-LTE) subframe is 6 ms in length by way of anexample.

FIG. 12 shows an example of a subframe for an NB-IoT (or NB-LTE) cellwhen an adjacent LTE cell uses TDD UL-DL configuration 1.

FIG. 13 shows an example of arranging a guard period in an NB-IoTsubframe.

FIG. 14 shows an example of subframes for an NB-IoT (or NB-LTE) cellwhen an adjacent LTE cell uses TDD UL-DL configuration 0.

FIG. 15 shows an example of subframes for an NB-IoT (or NB-LTE) cellwhen a neighboring LTE cell uses TDD UL-DL configuration 1.

FIG. 16 is a flow chart summarizing some of the embodiments of thepresent disclosure.

FIG. 17 is a block diagram illustrating a wireless communication systemin which an embodiment of the present disclosure is implemented.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, based on 3rd Generation Partnership Project (3GPP) longterm evolution (LTE) or 3GPP LTE-advanced (LTE-A), the present inventionwill be applied. This is just an example, and the present invention maybe applied to various wireless communication systems. Hereinafter, LTEincludes LTE and/or LTE-A.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the present invention includesthe meaning of the plural number unless the meaning of the singularnumber is definitely different from that of the plural number in thecontext. In the following description, the term ‘include’ or ‘have’ mayrepresent the existence of a feature, a number, a step, an operation, acomponent, a part or the combination thereof described in the presentinvention, and may not exclude the existence or addition of anotherfeature, another number, another step, another operation, anothercomponent, another part or the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

As used herein, ‘base station’ generally refers to a fixed station thatcommunicates with a wireless device and may be denoted by other termssuch as eNB (evolved-NodeB), BTS (base transceiver system), or accesspoint.

As used herein, ‘user equipment (UE)’ may be stationary or mobile, andmay be denoted by other terms such as device, wireless device, terminal,MS (mobile station), UT (user terminal), SS (subscriber station), MT(mobile terminal) and etc.

FIG. 1 illustrates a wireless communication system.

As seen with reference to FIG. 1, the wireless communication systemincludes at least one base station (BS) 20. Each base station 20provides a communication service to specific geographical areas(generally, referred to as cells) 20 a, 20 b, and 20 c. The cell can befurther divided into a plurality of areas (sectors).

The UE generally belongs to one cell and the cell to which the UE belongis referred to as a serving cell. A base station that provides thecommunication service to the serving cell is referred to as a servingBS. Since the wireless communication system is a cellular system,another cell that neighbors to the serving cell is present. Another cellwhich neighbors to the serving cell is referred to a neighbor cell. Abase station that provides the communication service to the neighborcell is referred to as a neighbor BS. The serving cell and the neighborcell are relatively decided based on the UE.

Hereinafter, a downlink means communication from the base station 20 tothe UE 10 and an uplink means communication from the UE 10 to the basestation 20. In the downlink, a transmitter may be a part of the basestation 20 and a receiver may be a part of the UE 10. In the uplink, thetransmitter may be a part of the UE 10 and the receiver may be a part ofthe base station 20.

Meanwhile, the wireless communication system may be generally dividedinto a frequency division duplex (FDD) type and a time division duplex(TDD) type. According to the FDD type, uplink transmission and downlinktransmission are achieved while occupying different frequency bands.According to the TDD type, the uplink transmission and the downlinktransmission are achieved at different time while occupying the samefrequency band. A channel response of the TDD type is substantiallyreciprocal. This means that a downlink channel response and an uplinkchannel response are approximately the same as each other in a givenfrequency area. Accordingly, in the TDD based wireless communicationsystem, the downlink channel response may be acquired from the uplinkchannel response. In the TDD type, since an entire frequency band istime-divided in the uplink transmission and the downlink transmission,the downlink transmission by the base station and the uplinktransmission by the terminal may not be performed simultaneously. In theTDD system in which the uplink transmission and the downlinktransmission are divided by the unit of a subframe, the uplinktransmission and the downlink transmission are performed in differentsubframes.

Hereinafter, the LTE system will be described in detail.

FIG. 2 shows a downlink radio frame structure according to FDD of 3rdgeneration partnership project (3GPP) long term evolution (LTE).

The radio frame of FIG. 2 may be found in the section 5 of 3GPP TS36.211 V10.4.0 (2011-12) “Evolved Universal Terrestrial Radio Access(E-UTRA); Physical Channels and Modulation (Release 10)”.

The radio frame includes 10 sub-frames indexed 0 to 9. One sub-frameincludes two consecutive slots. Accordingly, the radio frame includes 20slots. The time taken for one sub-frame to be transmitted is denoted TTI(transmission time interval). For example, the length of one sub-framemay be 1 ms, and the length of one slot may be 0.5 ms.

The structure of the radio frame is for exemplary purposes only, andthus the number of sub-frames included in the radio frame or the numberof slots included in the sub-frame may change variously.

Meanwhile, one slot may include a plurality of OFDM symbols. The numberof OFDM symbols included in one slot may vary depending on a cyclicprefix (CP).

FIG. 3 illustrates the architecture of a downlink radio frame accordingto TDD in 3GPP LTE.

For this, 3GPP TS 36.211 V10.4.0 (2011-23) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, Ch. 4 may be referenced, and this is for TDD (timedivision duplex).

Sub-frames having index #1 and index #6 are denoted special sub-frames,and include a DwPTS (Downlink Pilot Time Slot: DwPTS), a GP (GuardPeriod) and an UpPTS (Uplink Pilot Time Slot). The DwPTS is used forinitial cell search, synchronization, or channel estimation in aterminal. The UpPTS is used for channel estimation in the base stationand for establishing uplink transmission sync of the terminal. The GP isa period for removing interference that arises on uplink due to amulti-path delay of a downlink signal between uplink and downlink.

In TDD, a DL (downlink) sub-frame and a UL (Uplink) co-exist in oneradio frame. Table 1 shows an example of configuration of a radio frame.

TABLE 1 UL-DL config- Switch-point Subframe index uration periodicity 01 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U DD D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D

‘D’ denotes a DL sub-frame, ‘U’ a UL sub-frame, and ‘S’ a specialsub-frame. When receiving a UL-DL configuration from the base station,the terminal may be aware of whether a sub-frame is a DL sub-frame or aUL sub-frame according to the configuration of the radio frame

TABLE 2 Normal CP in downlink Extended CP in downlink Special UpPTSUpPTS subframe Normal CP Extended CP Normal CP Extended CP configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592*Ts 2192*Ts2560*Ts  7680*Ts 2192*Ts 2560*Ts 1 19760*Ts 20480*Ts 2 21952*Ts 23040*Ts3 24144*Ts 25600*Ts 4 26336*Ts  7680*Ts 4384*Ts 5120*ts  5  6592*Ts4384*Ts 5120*ts  20480*Ts 6 19760*Ts 23040*Ts 7 21952*Ts — 8 24144*Ts —

FIG. 4 illustrates an example resource grid for one uplink or downlinkslot in 3GPP LTE.

Referring to FIG. 4, the uplink slot includes a plurality of OFDM(orthogonal frequency division multiplexing) symbols in the time domainand NRB resource blocks (RBs) in the frequency domain. For example, inthe LTE system, the number of resource blocks (RBs), i.e., NRB, may beone from 6 to 110.

The resource block is a unit of resource allocation and includes aplurality of sub-carriers in the frequency domain. For example, if oneslot includes seven OFDM symbols in the time domain and the resourceblock includes 12 sub-carriers in the frequency domain, one resourceblock may include 7×12 resource elements (REs).

Meanwhile, the number of sub-carriers in one OFDM symbol may be one of128, 256, 512, 1024, 1536, and 2048.

In 3GPP LTE, the resource grid for one uplink slot shown in FIG. 4 mayalso apply to the resource grid for the downlink slot.

The physical channels in 3GPP LTE may be classified into data channelssuch as PDSCH (physical downlink shared channel) and PUSCH (physicaluplink shared channel) and control channels such as PDCCH (physicaldownlink control channel), PCFICH (physical control format indicatorchannel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH(physical uplink control channel).

The uplink channels include a PUSCH, a PUCCH, an SRS (Sounding ReferenceSignal), and a PRACH (physical random access channel).

FIG. 5 is a flowchart illustrating a random access procedure in 3GPPLTE.

The random access procedure is used for the UE 10 to achieve ULsynchronization with the base station, that is, eNodeB 20, or for UE toreceive UL radio resource assignment from the base station.

The UE 10 receives a root index and a physical random access channel(PRACH) configuration index from the eNodeB 20. Each cell has 64candidate random access preambles defined by a ZC (Zadoff-Chu) sequence.The root index refers to a logical index used for the UE to generate the64 candidate random access preambles.

The transmission of random access preambles is limited to specific timeand frequency resources for each cell. The PRACH configuration indexindicates a specific subframe available for transmission of the randomaccess preamble and a preamble format.

The UE 10 transmits an arbitrarily selected random access preamble tothe eNodeB 20. In this connection, the UE 10 selects one of the 64candidate random access preambles. Further, the UE 10 selects a subframecorresponding to the PRACH configuration index. The UE 10 transmits theselected random access preamble on the selected subframe.

Upon receiving the random access preamble, the eNodeB 20 sends a randomaccess response (RAR) to the UE 10. The random access response isdetected using two steps as follows. First, the UE 10 detects a PDCCHmasked using a random access-RNTI (R-RNTI). Then, the UE 10 receives therandom access response in a MAC (Medium Access Control) PDU (ProtocolData Unit) on a PDSCH indicated by the detected PDCCH.

<Carrier Aggregation>

A carrier aggregation system is now described.

A carrier aggregation system aggregates a plurality of componentcarriers (CCs). A meaning of an existing cell is changed according tothe above carrier aggregation. According to the carrier aggregation, acell may signify a combination of a downlink component carrier and anuplink component carrier or an independent downlink component carrier.

Further, the cell in the carrier aggregation may be classified into aprimary cell, a secondary cell, and a serving cell. The primary cellsignifies a cell operated in a primary frequency. The primary cellsignifies a cell which UE performs an initial connection establishmentprocedure or a connection reestablishment procedure or a cell indicatedas a primary cell in a handover procedure. The secondary cell signifiesa cell operating in a secondary frequency. Once the RRC connection isestablished, the secondary cell is used to provide an additional radioresource.

As described above, the carrier aggregation system may support aplurality of component carriers (CCs), that is, a plurality of servingcells unlike a single carrier system.

The carrier aggregation system may support a cross-carrier scheduling.The cross-carrier scheduling is a scheduling method capable ofperforming resource allocation of a PDSCH transmitted through othercomponent carrier through a PDCCH transmitted through a specificcomponent carrier and/or resource allocation of a PUSCH transmittedthrough other component carrier different from a component carrierbasically linked with the specific component carrier.

<IoT (Internet of Things) Communication>

Hereinafter, the IoT communication will be described.

FIG. 6A shows an example of IoT (Internet of Things) communication.

The IoT communication refers to the exchange of information between theIoT devices 100 without human interaction through the base station 200or between the IoT device 100 and the server 700 through the basestation 200. In this way, the IoT communication is also referred to asCIoT (Cellular Internet of Things) in that the IoT communication isperformed through the cellular base station.

This IoT communication may refer to a kind of machine type communication(MTC). Therefore, the IoT device may be referred to as an MTC device.

The IoT service is differentiated from the conventional communicationservice in which a person is involved. The IoT service may includevarious categories of services, including tracking, metering, payment,medical services, and remote controls. For example, the IoT services mayinclude meter reading, water level measurement, surveillance camerautilization, vending machine related inventory reporting, and so on.

The IoT communication has a small amount of transmitted data. Further,uplink or downlink data transmission/reception rarely occurs.Accordingly, it is desirable to lower a price of the IoT device 100 andreduce battery consumption in accordance with the low data rate. Inaddition, since the IoT device 100 has low mobility, the IoT device 100has substantially the unchanged channel environment.

FIG. 6B is an example of a cell coverage extension or enhancement forthe IoT device.

Recently, it is considered to extend or enhance the cell coverage of thebase station for the IoT device 100. To this end, various techniques forcell coverage extension or enhancement are discussed.

However, if the coverage of the cell is extended or enhanced, and whenthe base station transmits the downlink channel to the IoT devicelocated in the coverage extension (CE) or coverage enhancement (CE)region, the IoT device has difficulty in receiving the downlink channel.Similarly, when the IoT device located in the CE region transmits theuplink channel to the base station as the channel is, the base stationhas difficulty in receiving the uplink channel.

In order to solve this problem, the downlink channel or uplink channelmay be repeatedly transmitted on a plurality of subframes. Thetransmission of uplink/downlink channels repeatedly on the plurality ofsubframes is referred to as bundle transmission.

Thus, the IoT device or base station may receive the bundle ofdownlink/uplink channels on the plurality of subframes, and may decode apart or all of the bundle. As a result, the decoding success rate can beincreased.

FIG. 7A and FIG. 7B are views illustrating examples of a sub-band inwhich the IoT device operates.

In one approach to a low cost of the IoT device, as shown in FIG. 7A,the IoT device may use, for example, a sub-band of approximately 1.4 MHzregardless of a system bandwidth of the cell.

In this connection, the region of the sub-band in which the IoT deviceoperates may be located in a central region (for example, six middlePRBs) of the system bandwidth of the cell, as shown in FIG. 7A.

Alternatively, as shown in FIG. 7B, in order to multiplex the IoTdevices in one subframe, a plurality of sub-bands for the IoT devicesare allocated in one subframe, so that different sub-bands may be usedby different IoT devices. In this connection, most of the IoT devicesmay use sub-bands other than the sub-bands in the central region (e.g.,the middle six PRBs) of the system band of the cell.

The IoT communication operating on such a reduced bandwidth may becalled NB (Narrow Band) IoT communication or NB CIoT communication.

FIG. 8 shows an example of a time resource used for the NB-IoTcommunication on M-frames basis.

Referring to FIG. 8, a frame that may be used for NB-IoT communicationmay be referred to as an M-frame, and the length of the M-frame may beillustratively 60 ms. Further, a subframe that may be used for the NBIoT communication may be referred to as an M-subframe, and its lengthmay be exemplarily 6 ms. Thus, the M-frame may include ten M-subframes.

Each M-subframe may include two slots, and each slot may beillustratively 3 ms in length.

However, unlike what is shown in FIG. 8, a slot that may be used for theNB IoT communication may have a length of 2 ms. In this case, thesubframe may have a length of 4 ms and the frame may have a length of 40ms. Such a case will be described in more detail with reference to FIG.9.

FIG. 9 is another example of a time resource and a frequency resourcethat may be used for the NB IoT communication.

Referring FIG. 9, a physical channel or a physical signal transmitted onone slot in the uplink of the NB-IoT communication includes N_(symb)^(UL) SC-FDMA symbols in the time domain, and N_(sc) ^(UL) subcarriersin the frequency domain. The uplink physical channel may be divided intoan NPUSCH (Narrowband Physical Uplink Shared Channel) and an NPRACH(Narrowband Physical Random Access Channel). Further, in the NB-IoTcommunication, the physical signal may be NDMRS (Narrowband DeModulationReference Signal).

In the NB-IoT communication, during the T_(slot) slot, the uplinkbandwidth of the N_(sc) ^(UL) subcarriers is as follows.

TABLE 3 Subcarrier spacing N_(sc) ^(UL) T_(slot) Δf = 3.75 kHz 4861440 * T_(s) Δf = 15 kHz 12 15360 * T_(s)

In the NB-IoT communication, each resource element (RE) of a resourcegrid nay be defined using an index pair (k, 1) respectively indicating atime region and a frequency region in the corresponding slot. In thisconnection, k=0, . . . , N_(sc) ^(UL)−1, and 1=0, . . . , N_(symb)^(UL)−1.

In the NB-IoT communication, a resource unit (RU) is used to map theNPUSCH to the resource element (RE). The resource units (RU) may bedefined as successive subcarriers N_(sc) ^(RU), and successive SC-FDMAsymbols N_(symb) ^(UL) N_(slots) ^(UL).

In this connection, N_(sc) ^(RU), N_(symb) ^(UL) and N_(slots) ^(UL) maybe as follows:

TABLE 4 NPUSCH format Δf N_(sc) ^(RU) N_(slots) ^(UL) N_(symb) ^(UL) 13.75 kHz 1 16 7   15 kHz 1 16 3 8 6 4 12 2 2 3.75 kHz 1 4   15 kHz 1 4

In the above table, NPUSCH format 1 is used to transmit the uplink datachannel. Further, NPUSCH format 2 is used to transmit uplink controlinformation.

Symbols of a symbol block z(0), . . . , z(M_(symb) ^(ap)−1) aremultiplied by a amplitude scaling factor based on a transmission powerPNPUSCH. Then, the multiplied symbols z(0), . . . , z(M_(symb) ^(ap)−1)are mapped sequentially from z(0) to z(M_(symb) ^(ap)−1) to subcarriersallocated for transmission of the NPUSCH. The mapping for the resourceelement (k, l) starts at a first slot in an assigned resource unit (RU).Then, the resource element (k, l) is mapped in an increasing order froman index k to an index l. The NPUSCH may be mapped to one or moreresource units (RUs).

EMBODIMENTS OF THE PRESENT DISCLOSURE

Hereinafter, as used herein, a device that operates on a reducedbandwidth in accordance withlow-complexity/low-capability/low-specification/low-cost will bereferred to as an LC device or a BL (bandwidth reduced) device or anNB-IoT device. In this connection, according to an embodiment of thepresent disclosure, coverage extension/enhancement (CE) may be dividedinto two modes. In a first mode (also referred to as CE mode A),repeated transmission is not performed, or a small number of repeatedtransmissions are performed. In a second mode (also referred to as CEmode B), a large number of repeated transmissions are allowed. Which ofthe above two modes to be activated may be signaled to the NB-IoT device(or LC device or BL device). In this connection, parameters assumed bythe NB-IoT device for transmission and reception of the controlchannel/data channel may vary based on the CE mode. Further, the DCIformat monitored by the NB-IOT device may vary based on the CE mode.However, some physical channels may be repeatedly transmitted the samenumber of times irrespective of whether the CE mode A or the CE mode Bis activated.

As described above, when the system bandwidth is divided into severalsub-bands, only one NB-IoT device (or LC device or BL device) may besupported in one sub-band at one time point.

However, if multiple NB-IoT devices (or LC devices or BL devices) accessone sub-band, the base station needs to design an initial connectionprocedure for selecting or managing one NB-IoT device suitable for thecorresponding sub-band, and a corresponding transmission channel.Basically, the base station should be able to detect and identify theNB-IoT device via the initial connection procedure by the NB-IoT device,that is, the random access channel (RACH) transmission procedure by theNB-IoT device. In addition, the corresponding NB-IoT device must becapable of uplink synchronization via an initial connection procedure,i.e., a RACH transmission procedure.

Hereinafter, according to the present disclosure, a RACH design methodby the NB-IoT device and NB-IoT device selection method by base stationare proposed based on a case where RACH transmissions are allowed to bemultiplexed by a plurality of NB-IoT devices (or LC devices or BLdevices) and a case where RACH transmissions are not allowed to bemultiplexed by a plurality of NB-IoT devices (or LC devices or BLdevices).

1. A Case where RACH Transmissions are Allowed to be Multiplexed by aPlurality of NB-IoT Devices

The relative positions of multiple NB-IoT devices (or LC devices or BLdevices) relative to the specific base station on the network may bedifferent from each other. Therefore, the arrival times of the RACHs tobe received by the base station may be different due to the propagationdelay. In this situation, when each of a plurality of NB-IoT devices usethe same sequence as a RACH, the base station has no way of knowingwhether the RACHs are transmitted by a plurality of NB-IoT devices orone NB-IoT device transmits a RACH and the base station has received theRACH in a superimposed manner via multi-paths.

Therefore, when a plurality of NB-IoT devices (or LC devices or BLdevices) transmit RACHs at similar time points (or in the case oftransmitted RACHs being partially or wholly overlapped), the NB-IoTdevice transmitting the RACH arriving at the base station later in timemay be difficult to be detected by the base station. Further, even whena specific NB-IoT device transmits a RACH ahead of other NB-IoT devices,the base station receives the RACH of the specific NB-IoT device and theRACHs of said other NB-IoT devices in an overlapped manner. Thus,reception performance of the RACHs deteriorates, and therefore,reception of the RACH at that point in time may be difficult. Basically,a RACH refers to a transmission channel that may be transmitted by anNB-IoT device at the time of initial connection, and thus it is generalthat RACH transmissions by a plurality of NB-IoT devices may collidewith each other. Therefore, even when it is assumed that only one NB-IoTdevice is accessible on one sub-band, at least the RACHs used at theinitial connection need to be designed to be multiplexed by theplurality of NB-IoT devices.

The following are more specific examples as for RACH designs. Basically,each NB-IoT device (or an LC device or a BL device) may transmit theRACH at the timing according to the downlink synchronization resultingfrom synchronizing the downlink.

As a first example, a base station allocates a plurality of RACHresources on a time-domain. For example, the base station may configurea plurality of RACH transmission start positions within a basictransmission unit (for example, sample, symbol, slot, subframe, frame,etc.). In further detail, information about the starting subframe and/orslot and/or frame used by the NB-IoT device to initiate the RACHtransmission may be configured or predefined for each coverage class. Inone example, if the length of time used for transmission for coverageclass 1 is set to one subframe, a timing at which RACH transmission maybe initiated may be configured or designated as an “N” * subframe unit.In this connection, the base station may only transmit “N” as theconfiguration value. On the other hand, on the basis of each RACHtransmission length, RACH transmission start points of time may bedifferent between the coverage classes. Alternatively, the base stationmay configure these Ns differently between coverage classes. Inaddition, this N may be a value that changes at each retransmission. Inone example, when the timing at which the first RACH transmission maystart is set to 10*subframe units, the first RACH retransmission mayoccur every 5*subframe units. Furthermore, the second RACHretransmission may occur every 2*subframe units which is shorter thanthe timing in the previous retransmission. This is to give more RACHtransmission opportunities for each retransmission. This is also toprioritize the RACH retransmission over the initial transmission.

Alternatively, the RACH resources used for RACH initial transmission andretransmission may be configured differently.

The resource used for RACH initial transmission may be a subset of theresources that may be used for RACH retransmission. This may mean thatmore resources are available, as the number of retransmissionsincreases. Such a resource may refer to a time and/or frequency resourceor a code/preamble resource. Alternatively, it may also be considered toincrease the probability of RACH transmission success by increasing thepower used for RACH retransmission. In general, if the RACH transmissionfails despite the retransmission of the RACH, the RACH transmission maybe resumed after a predetermined time corresponding to the backoff haselapsed. Thus, after the predetermined period of time in accordance withthe backoff, the RACH transmission may be performed again using a firstavailable starting subframe and/or slot and/or frame. In thisconnection, the predetermined time period according to the backoff maybe configured as the smallest unit time. For example, one subframe maybe used as the unit time of the backoff, or one slot may be used as theunit time of the backoff. When there occurs a slot or subframe thatcannot be used to perform the RACH transmission after performing thebackoff, the NB-IoT device may perform a backoff again or may perform aRACH transmission using the next available resource.

This will be described below with reference to FIG. 10.

FIG. 10 shows a first example for multiplexing RACHs by a plurality ofNB-IoT devices.

As shown in FIG. 10, a plurality of NB-IoT devices (or LC devices or BLdevices) may select RACH resources so that the RACH resources do notoverlap with each other on the time axis, and then transmit the selectedRACH resources. This allows the base station to distinguish betweendifferent RACHs. Additionally, in order to prevent some overlap betweenRACH resources on the time domain, the present disclosure may considerintroducing a guard time. The RACH resources that are not overlappedwith each other on the time axis may be randomly selected between theNB-IoT devices, or may be configured based on pre-configured values suchas IDs of the NB-IoT device. In this connection, the random selectionscheme may be performed based on the random number generated by theNB-IoT device at the time of performing the RACH procedure. In oneexample, the NB-IoT device may generate a random number, and may againselect the RACH resources such as the RACH transmission timing and/orthe subcarrier index (or frequency position) and/or code (or preambleindex) based on the random number. In this case, the base station mayfind out what random number generated by the NB-IoT device based on theresources used to transmit the RACHs.

On the other hand, as a second example, a base station may allocate aplurality of RACH resources in a code-domain. Basically, it may beassumed that a plurality of NB-IoT devices (or LC devices or BL devices)may transmit RACHs composed of different sequences. The sequence may berandomly selected or preconfigured based on the ID, etc. of the device.

As a third example, the base station allocates multiple RACH resourcesin the frequency domain. Basically, frequency resources for multipleRACH resources are allocated within the system bandwidth. Differentfrequency resources may be allocated between NB-IoT device groups orbetween the coverage classes. More specifically, based on the basic RACHresource (UL sub-band corresponding to the DL sub-band used for PBCHreception, UL sub-band located at the same frequency in TDD, and ULsub-band located at the same position in the frequency spectrum in FDD),several PRACH resources may be used. A mapping between the coverageclasses and the available sub-bands may be carried out sequentially. Inon example, CE1(1), CE2(2), CE3(3), CE4(1), and CE5 (2) mappings may beachieved when there are three sub-bands and five coverage classes. Whenthe same coverage class is mapped to one sub-band, the resources may bedistinguished via TDM/CDM.

The RACH referred to in the above description may be represented by anUL synchronization sequence/signal, pilot, etc. Further, theabove-mentioned examples may be applied in combination. For example, inthe TDM scheme, overlapped RACH resources on the time axis may befurther distinguished via the CDM. In this case, the information aboutthe start subframe and/or slot and/or frame at which RACH transmissionmay be started may be configured or be pre-specified between thecoverage classes.

Moreover, in configuring the resources, the initial RACH transmissionresources and the RACH retransmission resources may be individuallyallocated. In one example, as for the initial transmission, the RACH maybe transmitted on a wide frequency resource using CDM, while as for RACHretransmission, the RACH may be retransmitted by selecting the frequencyband using the FDMA scheme. Conversely, the opposite may be possible.Alternatively, the FDMA scheme or the CDM scheme (preamble) may beselected between the coverage classes. Alternatively, the RACHtransmission scheme may vary depending on the capabilities of the NB-IoTdevices. The resource configurations for resource regions with differenttransmission schemes may be independent of each other. Alternatively, inthe case of an inband scenario, that is, when the operating carrier ofthe NB-IoT device is identical with the operating carrier of the legacyUE, the transmission scheme such as the CDM, etc. may be used. However,when the operating carrier of the NB-IoT device is non-identical withthe operating carrier of the legacy UE, FDMA may be selected, or atransmission mode may be designated.

On the other hand, although a plurality of NB-IoT devices (or an LCdevice or a BL device) may attempt to access the same sub-band at thetime of initial connection procedure in the next system, only one NB-IoTdevice per each band may be supported when starting actually sending orreceiving data. In this situation, it is necessary to design the NB-IoTdevice selection procedure more efficiently. For example, after the basestation receives and detects RACHs for a plurality of NB-IoT devices,the base station selects only some or one NB-IoT device and processesthe remaining procedures of the initial connection procedure only forthe selected devices. The following are more specific examples. In theexamples below, the RACH may be considered to be divided into asequence/signal portion for UL synchronization, and a data portion.

As a first example, before transmitting the data portion of the RACH,the base station selects some or one NB-IoT device (or LC device or BLdevice) based on the received RACHs. In this case, the base station maytransmit a response message to the NB-IoT device based on thesequence/signal transmitted by the selected NB-IoT device. The messagemay include parameters such as RACH resource, RACH sequence index, etc.Thereafter, a suitable NB-IoT device may transmit the data portion ofthe RACH to the base station.

As a second example, after the time of transmitting the data part in theRACH, the base station selects some or one NB-IoT device (or LC deviceor BL device) based on the received RACHs. In this case, there is a highpossibility of selecting an NB-IoT device suitable for the correspondingsub-band based on the data transmitted at the initial connection.However, a scheme for managing RACH data collision for various NB-IoTdevices may be required.

In the initial connection procedure, the criterion used when the basestation selects some or single NB-IoT device (or LC device or BL device)based on the plurality of received RACHs may include the RACH receptiontime (for example, a device corresponding to the RACH received first),and a type of the received RACH sequence. In this connection, the basestation selects the appropriate NB-IoT device to be supported in thecorresponding sub-band by selecting the criterion as channel quality,buffer status, device category, etc. in case of RACH resource. In thisconnection, the advantage of the base station selecting some or a singleNB-IoT device from the RACH procedure is as follows: When actuallyoperating in the FDMA mode, the number of NB-IoT devices that can besupported via one sub-band during a certain period of time may belimited. However, resources for the NB-IoT device can be saved bystopping the initial connection procedure in advance for the NB-IoTdevices that will not be selected for a long time via schedulingthereof.

When a plurality of initial connection procedures are allowed in onesub-band (after RACH transmission), it is necessary to manage RAR(random access) more efficiently. To this end, the base station mayconfigure a RACH reception window and an RAR window, and broadcast theconfiguration information to an NB-IoT device (or an LC device or a BLdevice). By including a control channel indicating the RAR into the RARwindow, the base station may transmit the control channel indicating theRAR. The base station may include RARs for all RACHs and some RACHsselected through the specified procedure as detected in the RACHreception window in one transmission channel in a bundling manner andthen may transmit the bundle.

In this case, it may also be considered to apply a further backoff atthe time of RACH (re) transmission. In this case, the backoffconfiguration may follow the manners described in section II below.

II. A Case when the RACHs are not Allowed to be Multiplexed by aPlurality of NB-IoT Devices

The RACH sequences may be allowed as the same sequence between differentNB-IoT devices (or LC devices or BL devices). In this regard, it may bepossible to consider reducing the likelihood of collisions betweenmultiple RACHs during the entire initial connection procedure.Basically, the scheme of configuring the backoff time at the time ofRACH (re) transmission initially or after collision may be considered.The case when the NB-IoT device can detect the collision presence orabsence may be assumed as a case when the device does not receive arandom access response (RAR), which is a response to the RACH from thebase station. The reference point of time when transmitting the RACH maybe designated in advance or may be specified in the form of systeminformation. The reference time point has the same value as when thebackoff time is set to 0, and may be repeated at regular intervals. Thebackoff time may be configured Between the NB-IoT devices, based onparameters including device category, channel quality, buffer status,etc. In addition, the backoff may be independently configured betweencoverage classes. Additionally or alternatively, the base station maytransmit the information about the backoff time to the NB-IoT device byincluding the information related to the backoff time in the systeminformation. The information on the backoff time may include an offsetvalue that may be referred to when configuring the backoff time, andwhether or not the RACH transmission is performed within a predeterminedinterval (for example, a frame in which system information istransmitted). The configuration may include configuring the actualbackoff time. Alternatively, the configuration may comprise configuringa maximum value and randomly configuring a backoff time based on themaximum value. In this case, the NB-IoT device may configure the backofftime to zero according to the urgency. Alternatively, the RACH for theNB-IoT device having the best channel state in consideration of FDMA maybe transmitted first so that the NB-IoT device having the best channelstate in consideration of FDMA may occupy the corresponding sub-band.For example, the NB-IoT device may detect system information transmittedby the base station (cell), and obtain information about RACHtransmission scheme and backoff time from the detected systeminformation. Then, the NB-IoT device may determine, based on theobtained information, the RACH transmission scheme for the frame periodcorresponding to the system information and transmit the RACH using thedetermined scheme. In general, it may be assumed that the systeminformation may be intermittently changed. Thereby, the systeminformation may further include a flag based on whether or not theinformation related to the RACH and/or the backoff time is changed. Thesystem information may further include a duration time during which theRACH and/or the backoff time configurations are maintained. In thelatter case, when the next system information is detected, the timer maybe changed/set based on the system information as recently received.When the NB-IoT device recognizes the change of the information via theflag or timer initialization, the device may not transmit the RACHwithin the frame in which the system information is detected in order toprepare for configuration change. Alternatively, the default value maybe applied during the configuration change period. In the case of thebackoff time, the default value thereof may be configured such that afinal value is 0 or an offset value as configured via the upper layersignal is 0. The flag may be configured in a toggle manner.

III. Frequency Hopping for RACH

The basic transmission unit of the RACH may be configured identicallyregardless of the coverage class. The basic transmission unit of thecorresponding RACH may be repeated based on the coverage classes. Inthis case, in performing RACH transmission based on single or multipleRACH basic transmission units, it is also possible to consider changingthe frequency position. In this connection, (1) the frequency positionto be included in RACH transmission may be confined within the samesub-band; (2) the NB-IoT device (or LC device or BL device) may performfrequency hopping for all or some region of the UL sub-bandcorresponding to the cell of the base station corresponding to theinitial connection (or receiving the RACH information).

IV. Operation after RACH Selection

When the base station selects one or more NB-IoT devices (or LC devicesor BL devices) within a specific sub-band (that is, when sufficientNB-IoT devices are allocated within a specific sub-band), the basestation needs to prevent access of a new NB-IoT device to the specificsub-band. When a new NB-IoT device continuously attempts an initialconnection, data from an already accessed NB-IoT device may beinterfered with by a RACH from the new NB-IoT device. Therefore, afterone or more NB-IoT devices are selected in the initial connectionprocedure, etc., it is necessary for the base station to prevent RACHtransmission in the corresponding sub-band.

To this end, the next system may configure messages for each sub-band,such as random access reject or overload indicator/information, etc. Inaddition, the random access reject or overload indicator information maybe configured between the coverage classes and/or between the RACHresources. Likewise, a message may be introduced to allow resumption ofrandom access in order to allow the access of a new NB-IoT device to thesub-band in consideration of the buffer state, etc. This message may beintroduced individually for each sub-band.

The random access reject or overload indicator/information may beconsidered to be managed in a more granular manner for the NB-IoT device(or LC device or BL device). In one example, the random access reject oroverload indicator/information may be managed based on the ID of theNB-IoT device and the random number generated by the NB-IoT device atthe initial connection. In a more specific example, random numbers maybe divided into multiple groups via a modulo operation, etc. Then, therandom access may be rejected for each divided group. Alternatively, theoverload may be configured for each divided group, or transmissionprobability, etc. may be specified for each divided group.

For example, it is assumed that the number of groups is 10, and eachgroup results from division of random numbers by a modulo operationvalue of 10. When it is configured to reject random access for groupsother than groups corresponding to the result of the modulo operationbeing equal to 5, only the NB-IoT device (or the LC device or the BLdevice) that generated the random number corresponding to the groupcorresponding to the result of the modulo operation being equal to 5 maytransmit the RACH during a certain period (i.e., a time period duringwhich random access is rejected). Collisions between RACHs within thesame group may be avoided via RACH resource allocation based on therandom number. Alternatively, overload indicator/information may beconfigured for each RACH resource. When the overload is indicated forthe RACH resource, the NB-IoT device may delay the RACH transmission orperform the backoff again. Alternatively, the overloadindicator/information may be differently configured between thesub-bands (or subcarriers). In this case, the NB-IoT device may resumethe RACH transmission only if the overload indicator/information is notconfigured for the sub-band (or subcarrier) that the correspondingdevice uses.

On the other hand, such overload indicator/information may not beconsidered for retransmission of the RACH. That is, the overloadindicator/information may not apply to the retransmission of the RACH.For example, when retransmission is performed more than a predeterminednumber of times, the NB-IoT device (or the LC device or the BL device)may perform the RACH transmission while ignoring the overloadindicator/information. Alternatively, the overload indicator/informationmay not be applied only in the case of the last retransmission, that is,only when the retransmission reaches the threshold count. The groups maybe divided according to the ID of each terminal or may be configuredaccording to the number of retransmissions.

As a simpler approach, whenever the backoff is configured, the counterfor the overload indicator/information is increased, and the RACHtransmission probability may be reduced to a certain degree for eachcounter for each overload indicator/information. For example, a backoffmay be transmitted per coverage class or sub-band (or subcarrier), andwhen backoff=0, the counter for the overload indicator/information maybe reset to zero. When the backoff is configured, the counter for theoverload indicator/information is increased, so that the RACHtransmission probability may be reduced, for example to be a probabilityof 10% for each counter for each overload indicator/information. If theoverload indicator/information=4, the RACH transmission is performedonly at a probability of 60%, thereby reducing the competition.

When the RACH transmission is interrupted for a relatively short periodof time for the purpose of network congestion control, etc., this timeperiod may be excluded from the time interval during which RACHretransmission is allowed. For example, if RACH retransmission isallowed for N time period, and RACH transmission is interrupted by thebase station during X time period, X time period is excluded from N timeperiod.

V. Coexistence with Other Systems

The band used to provide the CIoT service may occupy some of the bandsin which other systems currently operates. Further, in a situation whereanother system already operates in the corresponding band, it may beassumed that said another system and the CIoT service co-exist. Anoperation in such a situation may be called an inband operation. Forthis purpose, the CIoT structure may have a structure similar to that ofthe coexisting system. In order for the next system to coexist with theLTE system, the next system may take the CIoT structure as a structurein LTE. The corresponding CIoT scheme may be called NB (Narrowband)-LTEor NB-IoT. The next system considers the CIoT service based on the LTE.The next system considers scaling down subcarrier spacing as a way toutilize the LTE structure. In the LTE system, the subcarrier spacing is15 kHz, but in NB-IoT (or NB-LTE), subcarrier spacing may be reduced to2.5 kHz, which is ⅙ of 15 kHz, or to 3.75 kHz. In this case, six RBs maybe mapped, based on NB-IoT (or NB-LTE), within a 180 kHz regioncorresponding to the size of one RB based on LTE. Instead, in the timedomain, time resources may be increased six times as compared to LTE, asshown in FIG. 8.

In NB-IoT (or NB-LTE), in the case of PRACH transmission, reuse of theLTE-based scheme may be considered. However, since the subcarrierspacing is assumed to be 1.25 kHz for the PRACH transmission in the LTEbased system, scaling down the subcarrier spacing may not be suitable interms of frequency offset. Therefore, in the embodiment of this section,it is also assumed that subcarrier spacing is set to 1.25 kHz for PRACHtransmission in NB-IoT (or NB-LTE).

The generation of the PRACH preamble may be performed using a ZC(Zadoff-Chu) sequence, and the length of the sequence may be consideredto be 139. In this case, the region occupied by the PRACH preamble is173.75 kHz. Therefore, if the sub-band size is 180 kHz, a guard band of3.125 kHz may be assigned to both ends of the sub-band. Via thecorresponding guard band, interference between these systems LTE andNB-IoT (or NB-LTE) may be mitigated during coexistence between LTE andNB-IoT (or NB-LTE). For reference, a 139-length preamble sequence maycorrespond to reuse of a sequence used in PRACH format 4 for TDDsmall-scale cells in LTE. In this case, the root index value for theNB-IoT (or NB-LTE) PRACH preamble may be expressed using the followingtable. As the logical index increases, the CM (cubic metric) increases.

TABLE 5 Logical root Physical root sequence number u sequence number (inincreasing order of the corresponding logical sequence number)  0-19 1138 2 137 3 136 4 135 5 134 6 133 7 132 8 131 9 130 10 129 20-39 11 12812 127 13 126 14 125 15 124 16 123 17 122 18 121 19 120 20 119 40-59 21118 22 117 23 116 24 115 25 114 26 113 27 112 28 111 29 110 30 109 60-7931 108 32 107 33 106 34 105 35 104 36 103 37 102 38 101 39 100 40 9980-99 41 98 42 97 43 96 44 95 45 94 46 93 47 92 48 91 49 90 50 89100-119 51 88 52 87 53 86 54 85 55 84 56 83 57 82 58 81 59 80 60 79120-137 61 78 62 77 63 76 64 75 65 74 66 73 67 72 68 71 69 70 — —138-837 N/A

Further, even in the case of the cyclic shift (CS) value for the PRACHpreamble, candidates of PRACH format 4 in LTE may be reused. Thefollowing table shows an example of a cyclic shift (CS) unit value(N_(CS)). Additional CS may be considered in the following table. In oneexample, the present disclosure may consider 38 and/or 40 (aiming for 35km).

TABLE 6 zeroCorrelationZoneConfig N_(CS) value 0 2 1 4 2 6 3 8 4 10 5 126 15 7 N/A 8 N/A 9 N/A 10 N/A 11 N/A 12 N/A 13 N/A 14 N/A 15 N/A

The guard time (GT) is designed to overcome the propagation delay duringPRACH transmission. In this regard, in the case of CIoT, the radius ofthe target cell may be 35 km. In this case, to overcome the round triptime (RTT), a minimum value of 233 us is required for the GT. Similarly,in the case of a CP (cyclic prefix) of the PRACH, it is necessary toovercome the RTT. Further, additional gaps may be needed to overcome thedelay spread. In one example, the target delay spread may be 16.67 us,in which case, the minimum value of the CP length may be 250 us. Thelength of the preamble sequence excluding the CP and GT may be expressedby the reciprocal of the subcarrier space and may therefore be expressedas 800 us. In this case, when each of CP and GT is configured to be 250us, the minimum transmission period length required for PRACHtransmission may be configured to be 1.3 msec. In this case, since sucha length exceeds one subframe length based on LTE, the correspondingsystem may be difficult to coexist with LTE operating with TDD (in whichthere is no continuous multiple UL subframes) in the in-band manner. Asa measure for this case, it may be considered to additionally introducea PRACH format for NB-IoT (or NB-LTE). In this connection, the targetdelay spread is adjusted to 6.25 us and the target cell radius isconfigured to be approximately 14 km, so that the CPlength is adjustedto 103.13 us, the GTlength is adjusted to 96.88 us, and the totaltransmission period is set to 1 msec.

In the case of the NB-IoT (or NB-LTE) PRACH preamble having the minimumunit length of 1.3 msec, it may be considered to adjust the minimum unitlength to 1.5 msec as a scheme for increasing the GT or CP length. Forexample, if the length of a subframe in NB-IoT (or NB-LTE) is 6 msec(corresponding to 6 subframes based on LTE), the subframe may be dividedinto two 3 msec slots. Since the PRACH has a relatively shorttransmission period relative to the subframe/slot, it may be consideredto have a plurality of PRACH resources per subframe or per slot. In oneexample, an NB-IoT (or NB-LTE) PRACH resource may be specified at thebeginning and/or end of an M-SF. Alternatively, an NB-IoT (or NB-LTE)PRACH resource may be specified at the beginning and/or end of the slot.In this case, the number of PRACH resources per subframe may be from 1up to a maximum of 4 PRACH resources. This will be described withreference to FIG. 11.

FIG. 11 illustrates an example in which the number of PRACH resourcesper subframe is 4 when the NB-IoT (or NB-LTE) subframe is 6 ms in lengthby way of example.

Referring to FIG. 11, when the NB-IoT (or NB-LTE) subframe is 6 ms inlength, PRACH resources per subframe may be four including PRACHresource (a) to PRACH resource (d).

Assuming that the TDD-LTE cell and the NB-IoT (or NB-LTE) cell coexistin an in-band manner, the PRACH resource may be configured when aplurality of successive UL subframes based on the LTE standard areincluded in the same one slot on the basis of NB-IoT (or NB-LTE)standard or when a plurality of successive UL subframes on the basis ofNB-IoT (or NB-LTE) standard exists in 10 subframes (single radio frame10 msec) based on LTE standard. Meanwhile, when a TDD DL/ULconfiguration in which one UL subframe exists in a radio frame is used,another PRACH format may be used. As a more specific example, as shownin FIG. 11, when the LTE cell operates using TDD UL-DL configuration 1,two consecutive LTE UL subframes are allocated to the left slot based onNB-IoT (or NB-LTE), whereby only the (b) region may be configured as anNB-IoT (or NB-LTE) PRACH resource. In other words, the PRACH resourcefor NB-IoT (or NB-LTE) may be configured only for the regioncorresponding to the UL subframe on the LTE basis.

On the other hand, when TDD is used in NB-IoT (or NB-LTE) communication,the length of the subframe is not always fixed to 6 msec, but the lengthof the subframe may vary based on the TDD DL/UL configuration. In oneexample, when TDD UL-DL configuration 1 is used in NB-IoT (or NB-LTE)communication, the length of the subframe may be 2 msec, and only two ULsubframes may be included in one radio frame. Further, when TDD UL-DLconfiguration 5 is used, the length of the subframe may be 1 msec, andonly one UL subframe may be included in one radio frame. That is, in theNB-IoT (or NB-LTE) standard, a subframe may be a unit on which one PUSCHor PUCCH is transmitted. Such a unit may be varied based on the TDDDL-UL configuration, for in-band coexistence between both systems.

VI. Coexistence with LTE TDD System

As described above, when the NB-IoT (or NB-LTE) system coexists with theLTE TDD system in an in-band manner, not only the PRACH transmissionneed to be newly designed, but also the uplink channel and the downlinkchannel need to be newly designed. When in the NB-IoT (or NB-LTE)system, a subframe has a length of 6 msec, DL/UL interference occurs,thereby causing interference toward the UE and base stationcommunicating based on legacy LTE. Further, the NB-IoT (or NB-LTE)system may also suffer from performance degradation due to interferencefrom the LTE system.

Therefore, following solutions thereto are proposed.

VI-1. Scheme 1: Limit/Ignore Transmission

Briefly, when the NB-IoT (or NB-LTE) system operates, information (forexample, TDD UL-DL configuration) about a LTE cell coexisting in anin-band manner with the NB-IoT system) is transmitted to a correspondingNB-IoT device (or LC device or BL device) via the SIB. For example, itmay be assumed that an NB-IoT device and a base station operate using asub-frame of 6 msec length, and, the NB-IoT (or NB-LTE) base stationdoes not perform DL transmissions using a resource portion (totally orpartially overlapped symbols) overlapped with the UL subframe of anadjacent LTE system, and, as a result, the NB-IoT device may not expectto receive it. On the other hand, it may be assumed that the NB-IoTdevice does not perform uplink transmission using a resource portion(totally or partially overlapped symbols) overlapped with a downlinksubframe of an adjacent LTE system, and as a result, the NB-IoT basestation may not expect to receive it. More specifically, in the casewhere some NB-IoT (or NB-LTE) symbols are overlapped over a plurality ofsubframes of an LTE system, the amount of resources that cannot be usedmay become large, and, thus, present disclosure may reduce the number ofsymbols per a NB-IoT subframe by changing a CP length. In one example,the number of symbols may be 12 per NB-IoT subframe or may be 6 perNB-IoT slot.

VI-2. Scheme 2: Change of NB-IoT Subframe/Slot Unit

In another scheme, when determining the number of symbols included inthe subframe for the NB-IoT (or NB-LTE) system, the length of thesubframe for the NB-IoT (or NB-LTE) system may be specified as an X mseclength including N symbols instead of 6 msec, based on the LTE extensionCP (target delay spread is 16.67 us, whereby the number of symbols perslot is 6). The X value may vary according to the TDD UL-DLconfiguration of the coexistent LTE system, and the X value may be equalto the number of consecutive LTE UL subframes. When the X value is thesame regardless of the TDD UL-DL configuration, the X value may be setto 2. In this case, the LTE system or band that may coexist with theNB-IoT (or NB-LTE) system in an in-band manner may be limited. Morespecifically, the LTE system with which the NB-IoT (or NB-LTE) systemmay co-exist in an in-band manner may use TDD UL-DL configurations 2 and5. In addition, all or some of TDD UL-DL configurations 0, 3, 6 may beexcluded from TDD UL-DL configurations used by the LTE systemcoexisting, in an in-band manner, with the NB-IoT (or NB-LTE). The valueof N may be 2*X.

The NB-IoT (or NB-IOT) subframe/slot is not defined for a time regioncorresponding to a special subframe in an LTE TDD cell, and, thus, theIOT (or NB-LTE) base station and/or device (or LC device or BL device)may not send or receive anything. More specifically, the NB-IoT downlinkuses the downlink region of the LTE special subframe, while the NB-IoTuplink may not use the uplink region of the LTE special subframe. ThePSS may be transmitted on the LTE special subframe, which may cause alimitation in power boosting in the NB-IoT (or NB-LTE) system. Further,on a resource region that may be used to transmit SRS in the legacy LTEsystem, the NB-IoT device may not transmit the uplink channel. However,when the special subframe is used by the NB-IoT base station or NB-IoTdevice (or an LC device or a BL device) for additional resourceutilization, the present disclosure may consider bundling somecorresponding DL regions and UL regions with subframes/slots of NB-IoT(or NB-LTE) system respectively adjacent thereto, and managing/using thegenerated bundles. The bundle scheme may consider increasing the numberof symbols included in the subframe/slot of the NB-IoT (or NB-LTE)system by an amount as extended by the special subframe. In one example,if the number of symbols included in the downlink subframe for theNB-IoT (or NB-LTE) system is 14, and the downlink region that may beextended using the LTE special subframe corresponds to three symbols,the downlink subframe of the LTE system adjacent to the special subframemay be extended to include 17 symbols. Thus, channel mapping andtransmission may be performed based on this extension. The LTE cell andNB-IoT (or NB-LTE) cell co-existing in an in-band manner may havedifferent target cell radii. In this case, a guard period in the specialsubframe in the NB-IoT (or NB-LTE) system may be excessively large. Inthis case, it may be considered that the NB-IoT (or NB-LTE) cellutilizes a portion of the guard period as a downlink and/or an uplinkresource. In this regard, a portion of the guard period may be used as aseparate NB-IoT (or NB-LTE) subframe. As mentioned above, the portion ofthe guard period may be bundled with an adjacent NB-IoT (or NB-LTE)subframe thereto.

FIG. 12 shows an example of a subframe for an NB-IoT (or NB-LTE) cellwhen TDD UL-DL configuration 1 is used in an adjacent LTE cell thereto.

Referring to FIG. 12, when TDD UL-DL configuration 1 is used in anadjacent LTE cell to the the NB-IoT (or NB-LTE) cell, the NB-IoT (orNB-LTE) cell may configure the corresponding subframe so that thecorresponding subframe has a length of 2 msec.

In this case, each slot of NB-IoT (or NB-LTE) system may include twosymbols, and thus the subframe for the NB-IoT (or NB-LTE) system mayinclude a total of four symbols. With respect to the CP length and thedata length constituting each symbol, the data length may be 400 usecbased on the assumption that the subcarrier spacing is 2.5 kHz. Based onthis assumption, the CP length may be 100 usec.

However, when designing the actual CP length, 100 usec may be overly setwith considering the target delay spread. Therefore, it may beconsidered to reduce the actual CP length, and to place a portion of GTbehind each symbol.

FIG. 13 shows an example in which a guard period is arranged in anNB-IoT subframe.

As shown in FIG. 13, a specific period may be configured as a GT in asubframe for the NB-IoT (or NB-LTE) system. In one example, as shown inFIG. 13, the corresponding specific period may be arranged near the lastboundary portion of the subframe for the NB-IoT (or NB-LTE) system. TheGT may be defined as an entire uplink subframe or a portion of theuplink subframe (overlapping the end boundary portion of the LTE uplinksubframe). The secured GT may be used to prevent collision with SRS inthe legacy LTE system. In FIG. 13, by way of example, the length of theNB-IoT subframe is set to 2 ms.

To this end, the CP length may be configured as 6.25 usec or 16.67 usec.The remaining period (for example, 83.33 usec) may be configured as GT.As a result, it is possible to secure the transmitting of the SRS by thelegacy LTE UE.

In a similar manner, the concept of this scheme may be extended to otherTDD UL-DL configurations. In one example, when the number of consecutiveuplink subframes is 2 (that is, when TDD UL-DL configuration 4 isapplied), a subframe for the NB-IoT (or NB-LTE) system of a 2 msec unitmay be introduced as described above. Further, a subframe for the NB-IoT(or NB-LTE) system of a 3 msec unit may be introduced when there arethree consecutive uplink subframes (for example, when the TDD UL-DLconfiguration 0 or 3 is applied). In this case, the number of symbolsconstituting the subframe for the NB-IoT (or NB-LTE) system may beseven. This is configured in order to keep the number of symbols perslot constant in the NB-IoT (or NB-LTE) system. Alternatively, thenumber of symbols constituting the subframe for the NB-IoT (or NB-LTE)system may be set to six. This may be done by adjusting the CP length.As in the TDD UL-DL configuration 6, when the number of consecutiveuplink subframes exists in a plurality of numbers in a radio frame, acase when the consecutive uplink subframes are 2 may be combined with acase when the consecutive uplink subframes are 3. If the number ofconsecutive uplink subframes is 1 (there is no continuous uplinksubframe), the unit of the subframe for the NB-IoT (or NB-LTE) system isset to 1 msec, and the number of symbols is set to 2.

The symbols constituting the subframe for the NB-IoT (or NB-LTE) systemin the above manner may be further divided into a DMRS (demodulationreference signal) portion and a data portion at the time of ULtransmission (for example, PUSCH).

In one example, when the number of symbols constituting the subframe forthe NB-IoT (or NB-LTE) system is two, the first symbol may be allocatedas a DMRS symbol on a NB-IoT subframe basis. In this case, even when thesecond symbol is affected by the legacy SRS, the data region maybasically be protected via HARQ operation.

When the number of symbols constituting the subframe for the NB-IoT (orNB-LTE) system is 4, the second and/or third symbols may be designatedas the DMRS symbol. In this connection, if there are two DMRS symbols,frequency hopping may be performed on the NB-IoT (or NB-LTE) slot basis.This may be necessary to reflect channel environment that change overtime as the length of each symbol increases. Alternatively, both ends(first and fourth) symbols may be designated as DMRS symbols in order tobetter reflect the channel environment that may change on the time axisas the length of each symbol increases. Alternatively, in order toperform repetitive frequency hopping in the same pattern on the NB-IoT(or NB-LTE) slot basis, the DMRS symbol may be mapped to the first andthird symbols or to the second and fourth symbols.

In the case where the number of symbols constituting the subframe forthe NB-IoT (or NB-LTE) system is 6, the middle two symbols (third andfourth symbols) or both ends symbols (the first and sixth symbols) maybe mapped to the DMRS symbol. Alternatively, the middle symbols (secondand fifth symbols) may be mapped to the DMRS symbol on the NB-IoT (orNB-LTE) slot basis. More specifically, it may be possible to considerconfiguring the LTE system so that the DMRS symbol is transmitted on anLTE subframe or slot basis. In one example, the present disclosure mayalso map a DMRS symbol to an odd index or symbol at an even index.

When the number of symbols constituting the subframe for the NB-IoT (orNB-LTE) system is 7, the DMRS symbol may be mapped to the fourth or bothend symbols (the first and seventh symbols), or to the second and sixthsymbols, or to both ends symbols and the middle symbol (first, fourth,and seventh symbols) in order to comply with the legacy PUSCH structure.

VI-3. Scheme 3: Change of Subcarrier Spacing Unit

In another scheme, the subframe unit of the NB-IoT (or NB-LTE) cell maybe set to 1 msec, in consideration of the in-band coexistence with theTDD LTE cell, in the same manner as the LTE system. However, the presentdisclosure may consider changing the subcarrier spacing. The main reasonfor doing this is as follows: In the case of excessive scaling down ofsubcarrier spacing, the number of symbols transmitted for 1 msec islimited, and the overhead occupied by DMRS symbols may be large.Further, instead of changing the subframe structure of the NB-IoT (orNB-LTE) system based on the TDD UL-DL configuration, the subframestructure of the NB-IoT (or NB-LTE) may be configured based on 1 msec.Thus, in a situation where the NB-IoT (or NB-LTE) system coexists withthe TDD-LTE system, resource management may be facilitated. When scalingdown the subcarrier spacing excessively, the degree of coherence ofpower to a specific resource (hereinafter referred to as “powerboosting” degree) may be mitigated. The candidate subcarrier spacingthat may be considered in embodiments may include (15 kHz), 7.5 kHz, 5kHz, 3.75 kHz, 3 kHz (2.5 kHz). These candidate values may be uplinksubcarrier spacing for the NB-IoT (or NB-LTE) system when the NB-IoT (orNB-LTE) system coexists with the TDD-LTE system. In an alternative,these candidate values may be applied at all times. In the former case,signaling may be provided such that a plurality of subcarrier spacingsare configured. In this case, the NB-IoT device may determine asubcarrier spacing for a corresponding cell among the plurality ofsubcarrier spacings. Meanwhile, the length of the NB-IoT subframe may bedetermined based on the subcarrier spacing. For example, if thesubcarrier spacing is 15 kHz, the length of the subframe may bedetermined as 1 ms. However, if the subcarrier spacing is 3.75 kHz, thelength of the subframe may be determined to be 2 ms. Furthermore, thenumber of symbols included in the subframe may be determined based onthe subcarrier spacing. For example, the number of symbols thatconstitute a subframe of a 1 msec length for the NB-IoT (or NB-LTE)system is (14 or 12), 7 or 6, 4, 3, 2 depending on the subcarrierspacing. In this case, the DMRS symbol configuration for the PUSCH maybe described as in the II. Scheme section.

In this manner, the number of uplink subframes available continuouslymay be changed based on the TDD UL-DL configuration, and, thus, thenumber of OFDM symbols transmitted in the PUSCH/PUCCH may be changedbased on the configuration, or the subcarrier spacing may be changedbased on the configuration. The change value may be determined based onthe UL-DL configuration. In other words, based on the TDD UL-DLconfiguration, one transmission unit TTI may be 1 msec in the case ofdownlink, while in the case of uplink, the TTI may vary (for example,TDD UL-DL configuration 0=3 msec, TDD UL-DL configuration 1=2 msec, TDDUL-DL configuration 2=1 msec, etc.). In the case of downlink,transmission takes place over 1 msec, but transmission may be done overa longer TTI via resource allocation, etc. The minimum TTI may be 1msec. In general, the uplink TTI may be set to 1 msec so that the samesubcarrier spacing applies to all UL-DL configurations n. It may beassumed when the uplink TTI=2 msec that UL-DL configuration (forexample, UL-DL configuration 2), etc., which does not support the uplinkTTI=2 msec may be not configured for an NB-IoT (or NB-LTE) device. Whenthe uplink TTI=1 msec is supported, a TTI with two OFDM symbols may beconfigured. In this case, it may be assumed that 3 symbols TTI may beconstructed by adding one symbol thereto using preceding UpPTS and GP.In general, additional symbols may be constructed using the UpPTS andGP. Further, whether there is or not such a symbol addition may beconfigured by the network.

More specifically, uplink resources and PRACH transmission resources maybe configured based on the TDD DL/UL configuration as follows. This maybe applied when it should be used in conjunction with a TDDconfiguration, for example, using 15 kHz configured via multiples of3.75 kHz.

1) TDD UL-DL configuration 0: The arrangement between downlink subframesand uplink subframes is DSUUUDSUUU. When performing a 15 kHz numerologyfour-multiplication on the CP length, a single 3.75 kHz OFDM symbol maybe mapped to four OFDM symbols (in the case of 15 kHz). In this case,7+3=10 OFDM symbols may be mapped to 3 consecutive uplink resources,starting from the uplink subframe, without using the special subframe.Alternatively, when using the special subframe, a total of 11 OFDMsymbols may be mapped to three consecutive uplink resources using twoOFDM symbols of the special frame and the remaining two OFDM symbols. Anuplink may occur every 5 msec.

Possible options for this configuration are shown in FIG. 14.

In case of doubling the CP or mapping a smaller number of symbols, theadditional remaining portion may be used as a gap.

In order that being identical with each other between 2 msec and 1 msecUL structures, the DM-RS symbols may correspond to a third symbol, and afourth symbol or fifth symbol from a last symbol. Alternatively, theDM-RS position may be different between the configurations.

2) TDD UL-DL configuration 1:

As shown in FIG. 15, the DM-RS may appear at a middle symbol or it maybe used in the same way as the TDD UL-DL configuration 0.

3) TDD UL-DL configuration 2: it may be used in the same way as the TDDUL-DL configuration 0 by aligning three symbols to one UL subframe or byreducing the CP using UpPTS to arrange a gap. It may be assumed that thenumber of symbols is 3, 4, and 3, and, the DM-RS may appear at themiddle symbol.

4) TDD UL-DL configuration 3: The arrangement between downlink subframesand uplink subframes is DSUUUDDDD. As a result, uplink may be configuredon a 10 msec basis. This configuration may comply with the uplinkstructure used in 5 msec of TDD UL-DL configuration 0.

TDD UL-DL configuration 4: The arrangement between the downlinksubframes and the uplink subframes is DSUUDDDDDD. As a result, uplinkmay be configured on a 10 msec basis. This configuration may comply withthe TDD UL-DL configuration 1.

TDD UL-DL configuration 5: The arrangement between downlink subframesand uplink subframes is DSUDDDDDDD. As a result, uplink may beconfigured on a 10 msec basis. This configuration may comply with theTDD UL-DL configuration 2.

7) TDD UL-DL configuration 6: The arrangement between downlink subframesand uplink subframes is DSUUUDSUUD. A former 5 msec portion may complywith the TDD UL-DL configuration 0 while a latter 5 msec portion maycomply with the TDD UL-DL configuration 1. Alternatively, a former 5msec portion may comply with the TDD UL-DL configuration 0 and a latter5 msec portion may comply with the TDD UL-DL configuration 0, wherein inthe latter 5 msec portion, 3 symbols may be subjected to rate matching.Alternatively, a former 5 msec portion may comply with the TDD UL-DLconfiguration 1 and a latter 5 msec portion may comply with the TDDUL-DL configuration 1, wherein the former 5 msec portion may use onlysuccessive two uplinks. Alternatively, a former 5 msec portion maycomply with the TDD UL-DL configuration 2 and a latter 5 msec portionmay comply with the TDD UL-DL configuration 2. Alternatively, a former 5msec portion may comply with the TDD UL-DL configuration 1 and a latter5 msec portion may comply with the TDD UL-DL configuration 2 or viceversa.

Typically, the uplink slot is set to 2 msec. When the number of uplinksubframes is odd, a 2 ms uplink slot and a 1 ms uplink slot (includingonly 3 symbols) may be used. The 2 msec uplink slot may always start atan odd subframe index or at an even subframe index. The 1 msec uplinkslot may be regarded as one unit. In this connection, if one uplinkresource unit is composed of m 3.75 kHz UL subframes or slots, 2 msecuplink subframe and 1 msec uplink subframe may be considered as onesubframe or slot. Therefore, if resource units exists over foursubframes, there may be one resource unit within 10 msec in case of TDDUL-DL configuration 0; and in case of configuration 1, there is oneresource unit within 20 msec; and in the case of configuration 2, theremay be one resource unit within 20 msec.

Characteristically, it may be assumed that one DM-RS may appear within 1msec or may appear every three symbols. Alternatively, two DM-RSs mayappear within 2 ms or every 7 symbols. On the other hand, if 1 mseclength corresponds to 3 symbols, one DM-RS symbol may or may not appear.

VII. PRACH Transmission Unit (Depending on TDD Configuration)

The PRACH for the NB-IoT system may be transmitted in the TDD system, orthe PRACH may be interfered with or interfere with the TDD systemdepending on the surrounding cell environment. In this case, theinterference may be coped with. Thus, it is necessary to configure thePRACH resource only for the uplink region based on the specific TDDUL-DL configuration. In a simple manner, each length of the PRACHtransmission unit, which is a basic unit for the entire PRACHtransmission, may be designed to be less than or equal to 1 ms, and eachPRACH transmission unit may be assigned to the uplink region. Ingeneral, as the number of symbols constituting the PRACH transmissionunit increases, the performance of the PRACH detection by the basestation can be improved due to transmission repetition, extension of thesequence length, and the like. Therefore, the length of the PRACHtransmission unit or the number of symbols constituting the PRACHtransmission unit may be different depending on the number of availableuplink subframes or a length of the UL region (for example, defined in asymbol unit). More specifically, the uplink region may correspond to thenumber of consecutive uplink subframes configured based on the TDD UL-DLconfiguration or a corresponding time period thereto. Further, a timeperiod corresponding to UpPts may be included in the PRACH transmissionunit in accordance with the special subframe configuration. These PRACHtransmission units may be configured in different PRACH formats or maybe configured using configuration parameters from higher layer signals.Alternatively, these PRACH transmission units may be preconfigured basedon TDD UL-DL configuration and/or special subframe configuration.

The following illustrates a specific example of a PRACH transmissionunit according to consecutive uplink periods based on TDD UL-DLconfiguration (of 15 kHz subcarrier spacing). In the followingembodiments, for convenience of description, the subcarrier spacing forthe PRACH is set to 3.75 kHz. However, the present invention is notlimited to this. In the case of other subcarrier spacings, thetransmission units may be changed to an appropriate number of symbolsaccording to the uplink time periods as described below. If the timeperiod and the length of the PRACH transmission unit are not matched,(1) they may be aligned to the first or last boundary of the uplink timeperiod, including UpPts; or (2) They may be aligned to the first or lastboundary based on the group of continuous uplink subframes except UpPts.

VII-1.3 Uplink Subframes+0/1/2 Uplink Symbols

These PRACH transmission units may be expressed as 3 ms, 3.667 ms, and4.333 ms respectively. In the case of TDD UL-DL configuration, thesePRACH transmission units may correspond to the entire time period of #0,and former half frame periods of #3 and #6 respectively. Based on 3.75kH subcarrier spacing, these PRACH transmission units may correspond to9 or 11, 12 or 13, 15 or 16 symbols, respectively. When expressing thePRACH transmission units in a unit of ms, these PRACH transmission unitsmay correspond to 9 (2.4 ms), 12 (3.2 ms), and 15 (4 ms) symbols,respectively. More particularly, it may be considered to additionallyuse a portion of the transmission resource (for example, within onesymbol) as a guard period of the special subframe. In this case, thesePRACH transmission units including the guard period may correspond tosymbols of 12 (3.2 ms), 15 (4 ms), 17 (4.53 ms), or 18 (4.8 ms),respectively.

VII-2. 2 Uplink Subframes+0/1/2 Uplink Symbols

These PRACH transmission units may be expressed as 2 ms, 2.667 ms, and3.333 ms respectively. In the case of TDD UL-DL configuration, thesePRACH transmission units may correspond to the entire time period of #1,and a former half frame period of #4 and a latter half frame period of#6. Based on 3.75 kH subcarrier spacing, these PRACH transmission unitsmay correspond to 6 or 7, 9 or 10, 12 symbols, respectively. Whenexpressing the PRACH transmission units in a unit of ms, these PRACHtransmission units may correspond to 6 (1.6 ms), 9 (2.4 ms), and 12 (3.2ms) symbols, respectively. The CP may be set to one symbol. Moreparticularly, it may be considered to additionally use a portion of thetransmission resource (for example, within one symbol) as a guard periodof the special subframe. In this case, these PRACH transmission unitsincluding the guard period may correspond to symbols of 8 (3.2 ms), 9(2.4 ms), and 13 (3.4667 ms) respectively.

VII-3. 1 Uplink Subframes+0/1/2 Uplink Symbols

These PRACH transmission units may be expressed as 1 ms, 1.667 ms, and2.333 ms respectively. In the case of TDD UL-DL configuration, thesePRACH transmission units may correspond to the entire time period of #2,and a former half frame period of #5. Based on 3.75 kH subcarrierspacing, these PRACH transmission units may correspond to 3, 6, 6 or 8symbols, respectively. When expressing the PRACH transmission units in aunit of ms, these PRACH transmission units may correspond to 3 (0.8 ms)and 6 (1.6 ms) symbols, respectively. The CP may be set to one symbol.More particularly, it may be considered to additionally use a portion ofthe transmission resource (for example, within one symbol) as a guardperiod of the special subframe. In this case, these PRACH transmissionunits including the guard period may correspond to symbols of 4 (1.0667ms), 7 (1.8667 ms), and 9 (2.4 ms) respectively.

FIG. 16 is a flow chart summarizing some of the embodiments of thepresent disclosure.

Referring to FIG. 16, an NB-IoT cell signals information on a pluralityof subcarrier spacings to an NB-IoT device.

Meanwhile, when the neighboring LTE cell operates in the TDD scheme, theLTE cell transmits information on the TDD UL-DL configuration and theSRS configuration to the NB-IoT cell.

Then, the NB-IoT cell transmits the information on the TDD UL-DLconfiguration and the SRS configuration of the neighboring LTE cell tothe NB-IoT device.

The NB-IoT device determines a subcarrier spacing to be used for theuplink channel based on the transmitted information. In this connection,the subcarrier spacing may be determined as either 3.75 kHz or 15 kHz.

The NB-IoT device determines a subframe length based on the determinedsubcarrier spacing. If the subcarrier spacing is 3.75 kHz, the subframelength may be determined to be 2 ms. Further, when the subcarrierspacing is 15 kHz, the subframe length may be determined as 1 ms.

If a subframe to be used for transmission of the uplink channel ispartially overlapped with the subframe used for transmitting the SRS ofthe neighboring LTE device, the NB-IoT device transmits the uplinkchannel only on the remaining portion of the subframe except for a lastportion of the subframe.

In this connection, the last portion of the subframe that is excluded intransmission of the uplink channel may be used to secure the SRStransmission by the neighboring LTE device.

According to the foregoing, the NB-IoT device (or LC device or BLdevice) can effectively transmit the uplink channel.

The embodiments of the present invention described so far may beimplemented by various means. For example, embodiments of the presentinvention may be implemented in hardware, firmware, software or acombination thereof, and the like. More specifically, the descriptionshave been made with reference to the drawings.

FIG. 17 is a block diagram illustrating a wireless communication systemin which an embodiment of the present disclosure is implemented.

The base station 200 includes a processor 201, a memory 202 and atransceiver (or radio frequency (or RF unit) 203. The memory 202 isconnected to the processor 201 and stores various information fordriving the processor 201. The transmission/reception unit (or RF unit)203 is connected to the processor 201 to transmit and/or receive a radiosignal to the processor and/or from the processor. The processor 201implements the proposed functions, procedures and/or methods as definedabove. The operation of the base station as mentioned in theabove-described embodiments may be implemented by the processor 201.

A wireless device (e.g., an NB-IOT device) 100 includes a processor 101,a memory 102, and a transceiver (or RF unit) 103. The memory 102 isconnected to the processor 101 and stores various information fordriving the processor 101. The transmission/reception unit (or RF unit)103 is connected to the processor 101 to transmit and/or receive a radiosignal thereto and/or therefrom. The processor 101 implements theproposed functions, procedures and/or methods as defined above.

The processor may include an application-specific integrated circuit(ASIC), other chipset, logical circuitry, and/or data processing units.The memory may include read-only memory (ROM), random access memory(RAM), flash memory, memory cards, storage media, and/or other storagedevices. The RF unit may include a baseband circuit for processing theradio signal. When the embodiments are implemented in software, theabove-described techniques may be implemented with modules (procedures,functions, etc.) that perform the functions described above. The modulemay be stored in the memory and may be executed by the processor. Thememory may be internal or external in or to the processor, and may becoupled to the processor by various well known means.

Although in the exemplary system as described above, the methods aredescribed on the basis of a flowchart using a series of steps or blocks,the present invention is not limited to the order of the steps, and somesteps thereof may occur in different orders or may occur concurrently.Further, those skilled in the art will understand that the steps asshown in the flowchart are not exclusive, that other steps may beincluded, or that one or more steps in the flowchart may be deleted,without affecting the scope of the invention.

What is claimed is:
 1. A method for transmitting an uplink signal, themethod performed by a narrowband-internet of things (NB-IoT) device andcomprising: determining a time resource unit for transmitting the uplinksignal based on an uplink subcarrier spacing; and transmitting theuplink signal on the time resource unit to a base station, wherein thetime resource unit includes one or more slots including a plurality ofsymbols, wherein a predetermined time period in a slot is not used forthe transmission of the uplink signal, based on that the uplinksubcarrier spacing is 3.75 kHz.
 2. The method of claim 1, wherein thepredetermined time period is located at an ending part of the slot. 3.The method of claim 1, wherein the predetermined time period in the slotis used for a guard period, based on that the uplink subcarrier spacingis 3.75 kHz.
 4. The method of claim 1, wherein based on the uplinksubcarrier spacing, a length of the one or more slots included in thetime resource unit is determined to be 2 ms.
 5. The method of claim 1,wherein the predetermined time period in the slot is not used for thetransmission of the uplink signal, based on that the predetermined timeperiod in the slot is overlapped with a temporal resource used fortransmission of a sounding reference signal (SRS).
 6. The method ofclaim 5, further comprising: receiving information related to the SRS byhigher layer signaling.
 7. The method of claim 1, wherein thepredetermined time period in the slot is not used for the transmissionof the uplink signal to secure transmission of a sounding referencesignal (SRS).
 8. A narrowband-internet of things (NB-IoT) deviceconfigured for transmitting an uplink signal, the NB-IoT devicecomprising: a transceiver configured to transmit and receive a radiosignal; and a processor operatively coupled to the transceiver, whereinthe processor is configured to: determine a time resource unit fortransmitting the uplink signal based on an uplink subcarrier spacing;and control the transceiver to transmit the uplink signal on the timeresource unit to a base station, wherein the time resource unit includesone or more slots including a plurality of symbols, wherein apredetermined time period in a slot is not used for the transmission ofthe uplink signal, based on that the uplink subcarrier spacing is 3.75kHz.
 9. The NB-IoT device of claim 8, wherein the predetermined timeperiod is located at an ending part of the slot.
 10. The NB-IoT deviceof claim 8, wherein the predetermined time period in the slot is usedfor a guard period, based on that the uplink subcarrier spacing is 3.75kHz.
 11. The NB-IoT device of claim 8, wherein based on the uplinksubcarrier spacing, a length of the one or more slots included in thetime resource unit is determined to be 2 ms.
 12. The NB-IoT device ofclaim 8, wherein the predetermined time period in the slot is not usedfor the transmission of the uplink signal, based on that thepredetermined time period in the slot is overlapped with a temporalresource used for transmission of a sounding reference signal (SRS). 13.The NB-IoT device of claim 12, further comprising: receiving informationrelated to the SRS by higher layer signaling.
 14. The NB-IoT device ofclaim 8, wherein the predetermined time period in the slot is not usedfor the transmission of the uplink signal to secure transmission of asounding reference signal (SRS).